gen physio - GIT

• Gastrointestinal Tract (GIT)


  Function: Digestion and absorption of food (nutritive substances, vitamins, minerals, fluids) for the utilization of the body
• Nutritive substances and their digestive enzymes

  • Carbohydrates
  • Proteins and Nucleic Acids
  • Lipids
• Carbohydrates


  Digested by: Ptyalin or salivary amylase in the mouth, Pancreatic amylase in the small intestines, Sucrase and lactase in the small intestines for absorption
• Proteins and Nucleic Acids

  Digested by: Pepsin and gelatinase in the stomach, Proteolytic enzymes (trypsin, chymotrypsin, elastase, endopeptidases) from the pancreas and intestinal mucosa in the small intestines
• Lipids


  Digested by: Pancreatic lipase, pancreatic esterase, bile salts (from the liver) in the duodenum
• Nerve Supply


  Autonomic nervous system: Parasympathetic activity increases intestinal smooth muscle activity, Sympathetic activity decreases intestinal smooth muscle activity and causes sphincter contraction
• Major networks of nerve fiber

  • Myenteric nerve plexus (Auerbach's plexus) between the outer longitudinal and middle circular muscle layers
  • Submucous plexus (Meissner's plexus) between the middle circular layer and the mucosa
• Gastrointestinal Hormones


  • Gastrin
  • Cholecystokinin-Pancreozymin
  • Secretin
• Gastrin


  Hormone produced by G cells in the lateral walls of the glands in the lateral portion of the gastric mucosa and also on the duodenal mucosa. Actions: Stimulates gastric acid and pepsin secretion, stimulates growth of gastric mucosa, causes contraction of the gastroesophageal junction, stimulates calcitonin secretion, stimulates secretion of glucagon and insulin after a protein meal. Acid inhibits gastrin secretion (-) feedback mechanism.
• Cholecystokinin-Pancreozymin


  Actions: Produces contraction of the gallbladder, increases the secretion of pancreatic juice rich in enzymes, increases insulin secretion, produces contraction of pyloric sphincter. Secretion is stimulated by the presence of products of protein digestion and acid in the mucosa of upper small intestines.
• Secretin


  Secreted by glands in the mucosa of the upper portion of the small intestines. Actions: Causes the secretion of watery, alkaline pancreatic juice, decreases gastric acid secretion, inhibits gastric emptying and enhances the motility of small intestines and colon, augments the contraction of pyloric sphincter. Secretion is stimulated by the presence of food in the small intestinal mucosa.
• Activities of Pharynx


  Pharyngeal stage of deglutition: Moves bolus from oropharynx to laryngopharynx and into the esophagus, Closes air passageways
• Activities of Esophagus


  Esophageal stage of deglutition: Permits entry of bolus from larynx into the esophagus, Pushes bolus down in the course of esophagus, Permits entry of bolus into the stomach, Has mucus for smooth passage of bolus
• Pancreas


  Produces 1200-1500 mL of pancreatic juice (clear, colorless liquid consisting of: water, salts, sodium bicarbonate and enzymes). The sodium bicarbonate buffers the acidic gastric juices. Enzymes in pancreatic juice: Pancreatic amylase, Protein digesting enzymes (trypsin, chymotrypsin, carboxypeptidase, elastase), Principal triglyceride-digesting enzyme (pancreatic lipase), Nucleic acid digesting enzymes (ribonuclease & deoxyribonuclease)
• Liver


  Hepatocytes secrete 800-1000 mL of bile per day. Bile: Yellow brownish or olive green liquid with a pH 7.6 - 8.6, consists mostly of water and bile acids, bile salts, cholesterol, and phospholipid called lecithin, bile pigments and several ions. Bile salts have an important role in emulsification (breakdown of large lipid globules into suspension of droplets of about 1 nanometer in diameter). Liver functions: Carbohydrate metabolism, Lipid metabolism, Protein metabolism, Processing of drugs and hormones, Excretion of bilirubin, Synthesis of bile salts, Storage of glycogen, vitamins (ADEK), minerals, Phagocytosis: rbc wbc and bacteria
• Small Intestine


  The major events of digestion and absorption happen in the small intestine. Divided into 3 regions: duodenum (shortest), jejunum (empty region), ileum (joins the large intestine).

  
• Types of Movements of Small Intestine

  • Segmentations: Localized, mixing type of contraction that mixes chyme with digestive juice to bring food particles in contact with the mucosa for absorption
  • Migrating Motility Complexes: Pushes chyme down the small intestine
• Large Intestine

  Breaks down undigested carbohydrates, proteins and amino acids into products that can be expelled in feces. Mucosa maintains water balance, solidifies feces, absorbs some vitamins and some ions. Elimination of feces from the rectum is called defecation.